Temperature and composition dependent structural investigation of the defect perovskite series Sr1-xTi1-2xNb2xO3, 0 ≤ x ≤ 0.2

The crystal structure of the defect perovskite series Sr1-xTi1-2xNb2xO3 has been investigated over a range of temperatures using high-resolution synchrotron X-ray diffraction, neutron diffraction and electron diffraction. Three distinct regions were observed: 0 < x <= 0.125 was a solid solution of Sr1-xTi1-2xNb2xO3 with minor SrTiO3 intergrowth, 0.125 <x <= 0.2 was a pure Sr1-xTi1-2xNb2xO3 solid solution adopting the cubic perovskite type structure (Pm (3) over barm) and for x> 0.2 Sr0.8Ti0.6Nb0.4O3 and Sr3TiNb4O15 formed a two phase region. The cubic structure for Sr0.8Ti0.6Nb0.4O3 was stable over the temperature range 90-1248 K and the thermal expansion co-efficient was determined to be 8.72(9) x 10(-6)K(-1). Electron diffraction studies revealed diffuse scattering due to local scale Ti/Nb displacements and slightly enhanced octahedral rotations that did not lead to long range order. The octahedral rotations were observed to lock-in' at temperatures below similar to 75 K resulting in a tetragonal structure (14/mcm) with anti-phase octahedral tilting about the c-axis. (C) 2010 Elsevier Inc. All rights reserved.